Intra-peritoneal injections of ethanol (50 umoles/ml body water) Sodium D(-)lactate (25 umoles/ml body water), and pentobarbital (15mg/kg rat) into 48 hr fasted male wistar rats produced anesthesia in about 15 minutes. Compared to controls, rats under ethanol and sodium D(- )lactate and sodium pentobarbital anesthesia showed a significant 40 to 50% decrease in their brain mitochondrial redox potential as assessed from a change in the NAD+/NADH ratio. The cytosolic redox potential remained unchanged with a lactate/pyruvate ration ranging from 15 to 23. The cytosolic phosphorylation potential was not significantly different between the ethanol group, the D(-) and L(+) lactate groups, pentobarbital group and the controls. On the basis of a decreased mitochondrial NAD/NADH ration, the current working hypothesis is that ethanol, D-lactate and Na-pentobarbital all exert a common effect to induce anesthesia by causing a partially inhibition of electron transport. This suggestion would help explain why tissues like brain and heart accumulate NADH, even though in contrast to liver, they lack alcohol dehydrogenase.